A spin valve tunnel magnetoresistive thin film having an amorphous CoFeB as a ferromagnetic electrode and an MgO film having a NaCl structure as a tunnel barrier layer is disclosed in Nonpatent Literature 1. A CoFe layer is used as a first pinned magnetic layer and an amorphous CoFeB layer is used as a second pinned magnetic layer in such tunnel magnetoresistive thin film. Then, CoFe having a body-centered cubic structure is crystallized from amorphous CoFeB through annealing at high temperature, and an epitaxial relationship of CoFe (001) [110]//MgO (001) [100] is realized with a (001)-oriented MgO layer. Accordingly, a high TMR (Tunneling Magneto Resistance) effect as in theory can be obtained (refer to Nonpatent Literature 2).
However, the film thickness of a Ru layer that is generally used as a non-magnetic layer for exchange coupling is set to be thin so as to generate a high exchange coupling magnetic field between the first pinned magnetic layer and the second pinned magnetic layer. Specifically, the thickness is 0.7 to 0.9 nm, at which a 2nd peak of a RKKY (Ruderman Kittel Kasuya Yoshida) interaction is said to occur, as disclosed in Nonpatent Literature 3. Because of that, the thin Ru layer diffuses into the first pinned magnetic layer and the second pinned magnetic layer through annealing at a higher temperature than 360° C. or through annealing for a long time even at 360° C., and there has been a problem that the exchange coupling magnetic field cannot be generated (refer to Nonpatent Literature 2).
It is reported that the Ru layer has an effect to prevent a thermal diffusion of Mn from an anti-ferromagnetic layer, which is used as the anti-ferromagnetic layer, made of a Mn alloy (refer to Nonpatent Literature 4).
According to a report from Lee et al, it has been found that heat resistance can be increased by increasing the thickness of the Ru layer, and that the MR (magnetoresistance) ratio can be further increased through annealing at high temperature.
However, it is not practical because an increase of the Ru film thickness decreases the exchange coupling magnetic field based on the RKKY interaction. Especially, because a high temperature process beyond 350° C. is included in the manufacturing process of magnetic random access memory, the above-described problem is serious.    Nonpatent Literature 1: D. Djayaprawira et al, Applied Physics Letters, 86, 092502(2005)    Nonpatent Literature 2: Y. S. Choi et al, Applied Physics Letters, 101, 013907 (2007)    Nonpatent Literature 3: Hasegawa et al, Journal of the Magnetic Society of Japan, vol. 24, No. 9, 1239 (2000)    Nonpatent Literature 4: Y. M. Lee et al, Applied Physics Letters, 89, 042506 (2006)